Stroke is the second leading cause of death and a major cause of disability in the world. This clinical syndrome is characterized by rapidly developing symptoms and/or signs of focal or global loss of cerebral function with no apparent cause other than that of vascular origin. Blood brain barrier (BBB) breakdown and brain (cerebral) edema with subsequent increase in intracranial presume is the major cause of death in stroke patients. The BBB consists of endothelial cells, pericytes, astrocytes, and the vascular basement membrane. Its main function is to form a tight barrier that regulates the entry of selected molecules from the blood into the central nervous system (CNS), and to prevent the passage of potentially harmful substances into the brain. The regulation of BBB permeability is a necessary part of normal physiology; however, as mentioned above in pathologic situations such as acute cerebral ischemia, excessive increases in vascular permeability lead to opening of the BBB and vasogenic edema (Garcia J. H. et al., Acta Neuropathol. (Berl) 43:85-95 (1978), and Baker, R. N et al., J. Neuropathol. Exp. Neurol. 30:668-679 (1971)).
Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) is a member of the tumor necrosis factor (TNF) superfamily of cytokines. TWEAK is initially synthesized as a type II transmembrane protein but can be cleaved to generate a 17-kDa soluble factor with biological activity (see FIG. 1 and Chicheportiche, Y. et al, J. Biol. Chem. 272:32401-32410 (1997)). Soluble TWEAK induces various cellular responses when it is added to cells in culture. TWEAK activity is mediated via binding to fibroblast growth factor-inducible 14 (Fn14), a member of the TNF receptor superfamily (see. e.g., Wiley, S. R. et al., Cytokine Growth Factor Rev. 14:241-249 (2003)). The Fn14 gene is expressed in a variety of cell and tissue types (supra). In addition, Fn14 gene expression is up-regulated following growth factor stimulation of quiescent cell cultures and after injury to the blood vessel wall or the liver (Wiley, S. R. et al., Immunity 15:837-846 (2001); Feng, S. L. et al., Am. J. Pathol. 156:1253-1261(2000)).
It has been shown that TWEAK binding to Fn14 activates the NF-κB (see e.g., Brown, S. A. et al., Biochem. J. 371:395-403 (2003)), extracellular signal-regulated kinase (ERK) and c-Jun NH2-terminal kinase (JNK) signal transduction pathways (see e.g. FIG. 2 and Donohue, P. J. et al., Arterioscler. Thromb. Vasc. Biol., 23:594-600 (2003).
The neurovascular unit (NVU) is a dynamic structure consisting of endothelial cells, the basal lamina, the astrocytic foot processes, the pericyte and the neuron. During cerebral ischemia, disruption of the NVU results in the development of cerebral edema (Baker R. N. et al., J. Neuropathol. Exp. Neurol. 30:668-679, (1971)). NF-κB is expressed at low levels in the CNS (Kaltschmidt C. et al., Mol. Cell Biol. 14:3981-3992 (1994)). It has been reported that NF-κB activity is significantly increased in animal models of ischemic stoke and data obtained from mice deficient in the NF-κB p50 subunit indicates that NF-κB activation enhances ischemic neuronal death (Schneider, A. et al., Nat. Med. 5:554-559 (1999)). NF-κB signaling and NF-κB-inducible gene products have been implicated in increased BBB permeability and cell death during cerebral ischemia (Xu, L. et al., Biochem. Biophys. Res. Commun. 299:14-17 (2002); Nadjar A. et al., J. Neurochem. 87:1024-1036(2003)).
Several TWEAK-inducible genes, such as IL-8, IL-6, MCP-1, GM-CSF, MMP-9, ICAM-1 and RANTES, are known to be regulated via the NF-κB pathway (see e.g., Lynch, C. N. et al., J. Biol. Chem. 274:8455-8459 (1999); Kim, S. H. et al., Circ. J. 68:396-3991 (2004); Jin, L. et al., J. Invest. Dermatol. 122:1175-1179 (2004); Mattson, M. P. and Carnandola, S. J. Clin. Invest. 107:247-254 (2001). It has been demonstrated that IL-6 and MMP-9 play a central role in the development of cerebral edema and the increase of permeability of the BBB, respectively (Pantoni, L. et al., Arterioscler. Thromb. Vasc. Biol. 18:503-513 (1998); Romanic, A. M. and Madri, J. A., Brain Pathol. 4:145-156 (1994)). It has also been reported that inhibition of IL-1 and IL-8 during cerebral ischemia results in a significant decrease in cerebral edema (see e.g., Rothwell, N, et al., J. Clin. Invest. 100:2648-2652 (1997); Matsumoto, T. et al., Lab. Invest. 77:119-125 (1997)).
In summary, disruption of the BBB with vasogenic edema is the most common cause of neurological deterioration and death following acute stoke. Although the use of tPA has been approved by the FDA for thrombolysis in patients with acute stroke, only a limited number of patients seem to benefit from this form of treatment (The National Institute of Neurological Disorders and Stroke t-PA Stroke Study Group, N. Engl. J. Med. 333:1581-1587 (1995)). Therefore, there remains a long-felt need in the art for identification of new therapeutic molecules that ameliorate cerebral ischemia-induced BBB breakdown and subsequent cell death and serve as new therapeutic agents for patients suffering from stroke and/or cerebral edema.